Certain fuel contaminants can accelerate corrosion in components associated with a gas turbine. Liquid fuels used for combustion in gas turbines typically include distillates and ash-bearing hydrocarbon-based fuels. Contaminants may be present in the fuel and may cause degradation of tanks, pipes, valves, alloy coatings, and other components associated with the delivery of fuel and the operation of the gas turbine. Salt water, sulfur, sodium, vanadium, potassium, calcium, lead, etc. may act alone or in combination to cause corrosion. For example, oxides of sulfur and vanadium may react with other contaminants to form sulfates and vanadates that are corrosive at high temperatures.
Typically, the presence of contaminants in fuel can damage protective oxide layers on the surface of gas turbine components such as combustors, transition pieces, turbine buckets, and other components in the hot gas path (HGP). Furthermore, contaminants in the compressor inlet air, injected steam, and water may contribute significantly to corrosion. Excessive corrosion can lead to component failure, resulting in major turbine component replacement, costly repairs and significant machine down time. Low-level quantities of certain corrosive elements (1 part per million or greater) in the fuel are sufficient to cause hot corrosion.
Detecting and quantifying the full complement of liquid fuel contaminants in their elemental form in a continuous on-line, real-time basis is technologically challenging, and has been explored through conversion of laboratory-grade methods to field-deployable equipment including X-Ray Fluorescence (XRF), Pulsed Neutron Activation Analysis (PNAA), Rotating Disk Electrode Atomic Emission Spectroscopy (RDE-AES), Electron Paramagnetic Resonance (EPR) and Inductively Coupled Plasma (ICP). The leading technology for this type of measurement is XRF for which several vendors have supplied on-line real-time systems capable of measuring hydrocarbon-based liquid fuels, with the primary focus on measuring sulfur in refinery fuel for the purpose of achieving ultra-low sulfur diesel. These on-line XRF systems may be able to detect the heavier metal contaminants (vanadium and lead) to the single-digit parts per million levels; however, these XRF systems do not appear capable of detecting the lighter metals (sodium, potassium, or calcium) at low levels.